What To Know About Performance Wheels and Tyres

PART FOUR: A set of aftermarket wheels and tyres can transform the look of a vehicle, but do they make a positive contribution to the handling and performance? RobHawkins investigates.

The acceleration, handling, cornering and braking ability of a vehicle can be vastly improved with a set of lightweight alloys and a good set of tyres. But the choice of wheels and tyres can seem like a minefield, especially if you consider buying second-hand. There are numerous points to consider when choosing a different set of wheels and tyres, as we’ve learnt by our mistakes on many an occasion, having often bought project cars with the wrong combination of wheels and tyres fitted.

If you want the best results from upgrading your wheels and tyres, then a brand new set of lightweight alloys from a specialist manufacturer is the answer, along with a reputable brand of tyre that’s light, low on noise and offers maximum grip. In the real world, however, we tend to look for short cuts, because such a package can easily cost more than the value of the vehicle.

This modification guide outlines the many potential pitfalls when shopping around for wheels and tyres, whether you’re buying new or second-hand. We explain the finer points of wheel and tyre specifications, and explain what happens when the wrong spec is fitted.

If you decide to buy second-hand wheels, there are a number of wheel refurbishers who can make them look as good as new, but the final bill can sometimes be costly, so we reveal a few DIY techniques that are a lot cheaper.

Finally, wheel upgrades aren’t solely for alloys. Steel is back in fashion, particularly widened wheels, so we’ve been to a specialist to find out what’s involved in banding.

WHEEL & TYRE JARGON BUSTER

Bead The internal circumference of the tyre that is in contact with the rim.

Cords Used in the construction of a tyre to help make it stiff. Modern radial tyres use steel cords in the tread.

Crossply Older style of tyre that was fitted to vehicles up to the 1960s.

Kingpin inclination

An imaginary vertical line drawn from the kingpins or balljoints on the uprights down to the ground. The line should settle somewhere in the middle of the tyre. If it’s further in, the steering will be heavier.

Offset The distance in millimetres between the centreline of the wheel and the wheel mounting face on the hub. Important when buying aftermarket wheels.

PCD Pitch circle diameter. Imagine drawing a circle that travels through the centre of a wheel’s bolt-holes. The diameter of this circle is the PCD of the wheel and is measured in millimetres. A PCD of 4x100 means there are four wheel bolts/nuts and the diameter of the aforementioned circle is 100mm.

Profile The height of the tyre wall (sidewall) as a percentage of the width of the tyre. A profile of 30 means the height of the tyre wall is 30% of the width of the tyre.

Radial Modern tyre design consisting of a sidewall and tread that are separately constructed.

Sidewall The side of a tyre. The height of this is called the profile (see above). Some tyres have markings for rotation and inside or outside.

Spigot ring Where the centre of the wheel sits on the hub. This supports the wheel and the wheel bolts secure the wheel in position.

Tracking The angle of the wheels in relation to each other when pointing straight ahead. Measurements are taken on the outside of the wheel at the frontmost and rearmost points.

TWI Tread wear indicators. Look for square-shaped markers between the treads. When the tread has worn down to these markers, this area of the tyre has reached the minimum depth.

WORN TYRE RULES

TYRE SPEC EXPLAINED

175 The width of the tyre in millimetres.

65 The height of the tyre wall as a percentage of its width; known as the profile. In this case, 65% of 175mm is 113.75mm.

R Signifies the tyre is a radial type.

15 The diameter of the wheel required to fit the tyre. This is measured in inches.

84 The load rating. A rating of 84 indicates a maximum load of 500kg can be carried, although this may exceed the recommended load for the car.

H The speed rating, indicating the maximum speed at which the tyre should be run. H is 130mph.

In the UK, the minimum depth of tread allowed on a tyre is 1.6mm, but this must cover 75% of the tread from the centre outwards. So if the centre of the tread is below 1.6mm, the tyre must be changed.

Look for the rubber inserts in the tread. These are the tread wear indicators. If the tread is worn down to the same height as these indicators, renew the tyre.

SPEED & LOAD CODES

The speed rating of a tyre is indicated as one or two letters on the sidewall of the tyre. The chart illustrates the maximum speed at which the tyre has been tested for one hour.

The load rating or load index is a number ranging from 62 to 125 and represents the maximum weight in kilos that the tyre can support at the designated speed for one hour continuously: 62 is the lightest at 265kg, whereas 125 can support 1650kg. Most tyres are in the middle, at around 90, which represents 600kg. Note that this figure in kilos isn’t for the entire vehicle, so a 90-rated tyre can be used on something weighing more than 600kg.

WHEEL SPEC EXPLAINED

Weiss/White Painted white

5½ Width of the wheel in inches

J The required tyre bead profile

15 Diameter of the wheel in inches

H2 The wheel is designed to take a H-speed rated tyre

Other codes you may see:

ET 42 42mm positive offset, which means the hub mounting face is 42mm from the centre line of the wheel towards the roadside.

ARE BIG WHEELS BETTER?

SPACERS & STUD CONVERSIONS

When we acquired our Mazda MX-5 Mk2 project car in 2012, it had 17-inch aftermarket alloy wheels, which weighed a hefty 22kg each. We changed them for a set of 14-inch standard wheels, which weighed around 10kg each, and the difference was astounding.

Due to the reduced rolling radius of the smaller wheels and tyres, the MX-5 was faster, the speedo was more accurate and all the worrying vibrations we’d experienced when driving the car with the hard-top removed were eliminated. When we fitted a brand-new set of tyres and had the tracking checked, the handling and grip was also improved.

Spacers are sometimes the easiest solution for fitting larger wheels and tyres, helping to avoid fouling the arches and other parts of the vehicle. However, they put a greater strain on the wheel bearings and, in some cases, can affect the handling because they change the tracking.

BUDGET WHEEL RESPRAY

1. We had a set of four BRM alloy wheels that were starting to look a little tatty, but were too costly to refurbish with a chrome rim and two-tone colour. The wheel on the left is how they all looked, while the one on the right is after we’d refurbished it.

2. After donning a breathing mask, we started the refurbishment by scraping off all of the loose paint from the alloy wheels. We also used a wire brush to remove any aluminium oxide, then thoroughly cleaned the surfaces with panel cleaner.

3. All of the black areas of the wheel were painted in a non-glossy black metal paint. We didn’t apply an etch primer and didn’t buy a special black paint, just one that was suitable for applying to bare metal.

4. While the black paint covered the inside of the wheel, which is hidden, we also applied it to some of the exposed surfaces. Once the paint had dried, the finish was a matt black and has survived for over a year.

6. We applied a gun-metal grey ElastiWrap paint using a small roller. We discovered a sponge roller is the best, along with a small paint brush to reach into the corners. However, we weren’t too concerned about excess paint.

7. We applied three coats of ElastiWrap. Once they had dried, we found we could peel off any overpainted areas; this rubberised paint is easier to remove if it’s a thick layer. We also polished the rim of the wheel.

8. Our home-refurbished wheels took a few evenings to complete and the total cost of the materials came to less than £35, with lots left over. Had we bought an aerosol can of ElastiWrap, we would have spent less than £20.

OFFSET DISASTERS

The offset of a wheel is critically important, especially when you’re choosing to fit a set of aftermarket wheels. The offset represents a measurement in millimetres between the mating surface of the wheel where it sits on the hub and the centreline of the wheel.

When choosing an aftermarket set of wheels, try to keep to a similar offset. Using a hugely different

offset can affect the handling and steering.

Reducing the offset of the wheel (going more negative) increases the track width, so the wheels and tyres may stick out of the arches. Extensions will be required to pass the MoT.

LEAKY WHEELS

If one or more tyres on your vehicle are slowly deflating and there are no signs of any damage to the tyre then the cause of the problem could be down to the wheel. Try inflating the tyre to its recommended pressure, then pour some soapy water around where the tyre makes contact with the wheel (the bead). If any bubbles appear, you’ve found the cause of the leak.

The area where the tyre sits can be cleaned and resealed to reduce the risk of leaks. Remove the tyre, then use a wire brush attached to an electric drill to clean the wheel. Apply sealant before refitting the tyre.

ROLLING RADIUS

If you fit a set of wheels and tyres with a larger circumference or rolling radius than the standard wheels and tyres, the accuracy of the speedometer may be altered. Try checking it with a sat-nav or else drive past a speed check display on the side of the road. Speedometers generally over-read, so you may find the difference isn’t too much. If you are particularly concerned, specialists such as Speedy Cables can recalibrate most speedometers.

DIP & STRIP

If an alloy wheel is deeply scratched and scuffed, the only solution is to strip it, clean it and have it repainted. An alloy wheel refurbisher with sandblasting equipment should be able to complete this. Budget for around £50 per wheel.

Once the tyre has been taken off, the exterior finish on the alloy needs to be removed to be able to get down to the bare alloy. The exterior finish is usually removed by dipping the entire wheel in chemicals such as methyline chloride. This lifts the painted finish off the alloy.

After dipping, the chemicals need to be thoroughly washed off, ideally using a pressure washer. The wheel can then be blasted to remove any further finish on the surface of the alloy; a fine aluminium oxide grit is best suited for an alloy wheel as it produces a smooth finish. This is usually performed in a blasting cabinet.

Once the wheel has been sufficiently blasted, it can be painted.

MISSING CHUNKS

Kerbing an alloy wheel may sometimes result in a chunk of alloy being removed. If this happens, the wheel could be rescued by an alloy specialist welding a new piece of alloy into the hole. The wheel’s tyre will need to be removed before any welding can be done. Once the new alloy has been welded into position, the patch can be finished with an angle grinder, followed by a die grinder, to reform the original shape of the wheel, then finished off with P240 paper on a sander.